1. Field of the Invention
The present invention relates to a control device for a transmission, and more particularly, to control executed at the time of switchover of shifting mode.
2. Description of the Related Art
A continuously variable transmission capable of continuously varying its gear ratio, or what is called a stepless transmission, has hitherto been used in motor vehicles mounted with internal combustion engines. Such a stepless transmission has, as its shifting modes, a stepless automatic shifting mode in which the gear ratio is continuously variable, and a stepped manual mode in which the driver manually performs a shifting operation to select a specific gear train from among those having respective fixed gear ratios.
There has also been known a stepless transmission which is equipped with a plurality of gear trains with respective fixed gear ratios, as in a conventional stepped automatic transmission, and which has, as its shifting modes, a stepped automatic shifting mode in which a specific gear train is automatically selected in accordance with the vehicle speed and the throttle valve opening angle, besides a stepless automatic shifting mode in which the gear ratio is automatically varied in a continuously manner so that the internal combustion engine can be operated with optimum fuel efficiency (Japanese Examined Patent Publication No. H07-102791).
A control device for the transmission disclosed in the above publication is configured to switch the shifting mode between the stepless automatic shifting mode and the stepped automatic shifting mode in accordance with the vehicle speed and the throttle valve opening angle.
Let it be assumed that the transmission disclosed in the above publication is additionally equipped with the stepped manual mode, in addition to the stepless automatic shifting mode and the stepped automatic shifting mode. In this case, when the stepped manual mode is canceled by the driver while the vehicle is running in the stepped automatic shifting mode, for example, the stepless automatic shifting mode or the stepped automatic shifting mode is resumed as the shifting mode in accordance with the vehicle speed and throttle valve opening angle assumed at the time the stepped manual mode is canceled.
However, where either the stepless automatic shifting mode or the stepped automatic shifting mode is resumed as the shifting mode in accordance with the vehicle speed and throttle valve opening angle assumed at the time of cancelation of the stepped manual mode, the shifting mode resumed after the stepped manual mode is canceled by the driver may possibly differ from the shifting mode that had been selected before the stepped manual mode was set by the driver. Such a situation is not desirable because the difference in shifting mode possibly brings a feeling of strangeness to the driver.